Heat curing adhesive

ABSTRACT

An adhesive material having a long storage life is prepared by applying to a carrier, a coating composition comprising a blend of a solid epoxy resin, solid curing agent for the expoxy resin, a film-forming binder, and a dispersing medium and drying the coating to a tack-free film. The adhesive-coated carrier or the film without the carrier may be used to bond substrates by pressing the substrates together with the adhesive film between them at elevated temperatures.

[4 1 Mar. 27, 1973 [54] HEAT CURING ADHESIVE [75] Inventor: Robert A. LeCompte, Mountain Lakes,N.J.

[73] Assigneez National Starch Corporation, New York, NY.

22 Filed: Jan.11, 197l [21] Appl. No.: 105,644

[52] U.S. Cl ..156/3l3,l17/25,117/161 A, 156/306, 156/330, 260/33.6 EP,260/837 R, 260/879 [51] Int. Cl. ..C08d 9/10 [58] Field of Search..260/33.6 EP, 837 R, 879; 156/313, 306, 330; 117/25, 161 A [56]References Cited UNITED STATES PATENTS 3,496,250 2/1970 Czerwinski..260/33.6 EP X 3,239,478 3/1966 Harlan 2,385,920 10/1945 Jenkins..260/34.2

and Chemical OTHER PUBLICATIONS D. J. Duffin, Laminated Plastics,Reinhold, New York, (1958) PP- 163-465.

Primary ExaminerM0rris Liebman Assistant Examiner-S. M. PersonAttorney-James & Franklin [57] ABSTRACT An adhesive material having along storage life is prepared by applying to a carrier, a coatingcomposition comprising a blend of a solid epoxy resin, solid curingagent for the expoxy resin, a film-forming binder, and a dispersingmedium and drying the coating to a tack-free film. The adhesive-coatedcarrier or the film without the carrier may be used to bond substratesby pressing the substrates together with the adhesive film between themat elevated temperatures.

19 Claims, No Drawings HEAT CURING ADHESIVE This invention relates to anovel method of forming a thermosetting, one-component adhesive filmhaving a long shelf life. The adhesive film will develop a rigid, highstrength, thermoset bond rapidly at moderately elevated temperatures.

Two-component epoxy resins have been used in adhesive compositions forsome time due to their excellent adhesive properties. However, the useof thermosetting Z-component epoxy resins as adhesives involves a greatdrawback. The adhesive containing the mixed resin and the curing agentor hardener does not have a long shelf life. That is, the mixture ofepoxy resin and curing agent, even at room temperature, begins to reactas soon as mixed and becomes unuseable after only short periods of timeif highly reactive curing agents are used. This is undesirable asoftentimes it is desirable to store the premixed resin and curativebefore theadhesive composition is ready to be used. If slower reactingcuratives are used to extend the room temperature storage life of themixed components, the curing time as elevated temperatures is oftenprohibitively long (in excess of 1 hour). 1

It has now been discovered that an adhesive composition comprising athermosetting epoxy resin and hardener may be formulated so that a fastbond-may be achieved at moderate temperatures with short heating timeswhile the adhesive still retains long storage life at room temperature.

The novel method of this invention comprises coating or impregnating acarrier with a coating composition comprising a blend of aroom-temperature, solid epoxy resin, a room-temperature solid curingagent for said epoxy resin, a film forming binder, and a dispersingmedium and drying the coating to a tack-free film. The coated carrier orthe unsupported film removed from the carrier, if the carrier is arelease material, may then be used as an adhesive by merely pressing asubstrate to be bonded to the film at elevated temperatures.

The coating composition comprises a solid epoxy resin, solid hardener,binder and dispersing medium.

The epoxy resin may be a room-temperature solid epoxy resin thataverages more than one, 1,2-epoxy group per molecule. A broad range ofcompounds containing 1,2-epoxy groups have use in the adhesivecompositions of the present invention. These epoxy resins should besolids at room-temperature. The uncured resin should soften attemperatures above about 60C. or even 125C. or higher; and in theuncured state, even without other components present, they preferablyare sufficiently brittle at room temperature as to be pulverizable. Theymust average more than one 1,2-epoxy group per molecule forcrosslinkinguThe room-temperature-solid commercial varieties ofdiglycidyl ethers of polyhydric phenols, particularly the diglycidylether of bisphenol A, are preferably and commonly used. However,synthesized, internally-complex, 1,2-epoxy containing compounds are alsoused and their use achieves variation in the properties of the curedproducts. Epoxy-terminated polyesters and polyamides may also be used.Other examples of solid epoxy resins which may be used in the coatingcompositions are solid aromatic adducts of diglycidyl ethers ofbisphenol A (Epon U-52), solid diglycidyl ethers of bisphenol A such asEpon 1002 and Epon 1007. Tetrafunctional polyglycidyl ethers oftetraphenylene ethane such as Epon 1031, polyglycidyl ethers oforthocresolformaldehyde novolac such as Ciba ECN1299, blends oftetrabromo bisphenol A, bisphenol A and epichlorohydrin such as DOWDERSll octafunctional glycidyl ethers such as Celanese SU-8 and thelike.

The hardeners for the epoxy resins must also be solid at roomtemperature. Any room-temperature solid hardener or curing agent forepoxy resins may be used, such as heat-activatable aromatic or aliphaticpolyamines or their adducts. These polyamine compounds have at least twoprimary or secondary nitrogen atoms and a combined total of at leastthree active hydrogen atoms. Examples of these compounds are meta-,ortho-, and paraphenylene diamines, 4,4- methylene dianiline,diamino-diphenyl sulfone, 1,4- naphthalene-diamine, 3,4-toluene diamine,oxydianiline, triethylene, tetramine, tetraethylenepentamine andalicyclic polyamines. Other curing agents may also be used such assubstituted imidazole salts, anhydrides, substituted triazines, solidorganic acids, BF complexes, and the like.

The binder may be any film-forming non-liquid thermoplastic binder resinwhich is soluble or emulsifiable in the dispersing medium and will notchemically react with the epoxy resin or hardener so that their curingproperties are destroyed. By non-liquid it is meant to include materialswith viscosity at 25C. of greater than 1,000,000 c.p.s. Thus materialshaving lower viscosities would not be suitable as binders in thisinvention.

The binder is used to hold the epoxy particles and hardener particles onthe backing or carrier reducing contact between them. The binder must bethermoplastic so as not to interfere with the heat cure and flow of theadhesive during the laminating process. Some examples of film-formingthermoplastic binders are: polyethylene oxide, such as Union CarbidesPolyox WSRN-lO, thermoplastic acrylic resins, such as Rohm 8L HaasAcryloid F-lO, vinylethyl ether resins, such as Union Carbide's EDBN,styrene-butadienestyrene block copolymers, such as Shell ChemicalsKraton llOl, polyvinyl acetate; polyvinyl alcohol, and the like.

The dispersing medium is necessary to apply the film-forming binder.Although the solid particles of epoxy and hardener are much lessreactive with one another than are their liquid counterparts, somepremature cure is found when the particles are contiguous to oneanother. The use of the dispersing medium slows the premature cure bydecreasing the concentration of reactive particles and by causing thedissolved binder to surround each particle keeping it from intimatelycontacting other reactive particles. Any dispersing medium which is anon-solvent for both the epoxy and the hardener and a solvent ordispersing medium for the binder resin and is volatile so that it iseasily removable, may be used. As the dispersing medium is different foreach epoxy, hardener and binder that is used in this system, many commonsolvents may be used depending on the system.

Examples of some dispersing agents useful herein are water, aliphatichydrocarbons such as heptane, hexane, VM&P naphtha and the like,alicyclic hydrocarbons such as cyclohexane and the like, alcohols suchas ethanol, butanol and the like, polyfunctional alcohols such as theglycols, low boiling phthalates such as C H,(COOCH and the like.

The amount of hardener used in the composition, of course, depends onthe particular epoxy used and the amount of epoxy used. Generally, anamount sufficient to crosslink the epoxy is used.

The binder is generally present in an amount no greater than about 95percent by weight based on the total solids and usually greater thanabout 1 per cent by weight based on the total solids. Enough binder isnecessary to hold the epoxy and hardener on the backing or carrier or infilm form after the coating operation and to envelop the particles so asto protect them from contact with one another.

The amount of dispersing medium used may be varied greatly, but it ispreferred to use coating compositions comprising between about per centand about 99 per cent dispersing medium. If less than about 5 per centdispersing medium is used, the viscosity of the dispersion increases tounworkable levels at room temperature and if greater than 99 per centdispersing medium is used, excessive quantities of the dispersion mustbe coated to produce a useable film.

In general, the preferred method of preparing the adhesive composition,is to grind the solid epoxy resins into small particles and admix thedispersing medium and binder, and then adding the powdered curirigagent. The dispersed powders may then be milled to a fine particle size,or simply mixed if the powders are already fine enough when they areadded to the composition. The preferred average particle size is lessthan 0.032 inch. Finely powdered epoxy resin and hardener are necessaryto insure good mix during the period of melt and flow as the adhesivecomposition is being hot pressed.

The adhesive composition may also contain various other materials suchas fillers, pigments, dyes, other types of thermosetting andthermoplastic resins, and the like.

The carrier may be coated or impregnated with the adhesive compositionusing any of the well-known coating methods, such as spraying,roll-coating, curtain-coating, dip-coating, and the like. The thicknessof the coating may vary widely but generally it is preferred to use athickness of from about 0.5 mils to about 100 mils, or thicker ifa thickcarrier is to be impregnated.

If preferred, the carrier may be coated on both sides or impregnatedwith the adhesive composition and the coated or impregnated carriercould be used as a crossband material where materials could be bondedtogether by pressing both materials to both sides of the coatedcrossband and heating to form a laminate.

It is noted that by the term impregnating" we mean also, the addition ofthe compositions to the carrier material prior to the formation of thecarrier material. Thus an asbestos paper or other fibrous material maybe impregnated by preparing a slurry of asbestos fibers in water andadding the composition of this invention and subsequently forming theasbestos sheet by applying the slurry to a screen and drying to a sheetform. In this way, an impregnated asbestos sheet is formed. Of course,this method also could be used to impregnate glass fiber mats byadmixing the compositions of this invention to the glass fiber slurryand forming a mat out of the composite.

The carrier to which the adhesive composition is applied may be anysheet material. It may be release paper, such as silicone-coated paper,and the like, or it could be polyethylene, wood veneer,resin-impregnated paper, fabrics, cloth, non-woven glass mat, wovenglass fabric, untempered hardboard, and the like. The preferred backingis non-woven glass mat.

The adhesive composition is applied to the carrier and then dried todrive off the dispersing medium leaving the epoxy resin particles andhardener particles encased in the binder resin. The adhesive compositionmay be dried by forced warm air at a temperature below the softeningpoint of the binder resin and the other components of the composition.

The coated carriers may then be stored for long periods prior to theiruse as a component for forming laminates.

The laminates are formed by hot-pressing a substrate to the coatedcarrier or crossband. If the carrier is coated on both sides orimpregnated, two substrates may be laminated together by merely placinga substrate on either side of the coated carrier or adhesive film andsubjecting to a hot-press cycle. The substrates will form strong bondswith the coated carrier or to each other.

The laminating may be carried out by inserting the composite of coatedcarrier and substrate or substrates in a press at about 200F to about400F, at a pressure of from about 10 pounds per square inch to about1,000 pounds per square inch for a period of from about 20 seconds toabout 10 minutes or more, depending on the cure time the epoxycomposition requires.

Many substrates may be used as materials to be bonded. Some examples arewood, wood veneer, paper, metals, felt, glass, plastics, masonry,ceramics, particle board, and the like.

The adhesive-coated-carrier may also be used to form multi-layer, orsingle layer, high strength rigid, internally reinforced, structuralsheet materials, useful for translucent building panels, electricalinsulators, molded chair shells, furniture parts and the like. To formthese structural objects the resin-coated or impregnated carrier ishot-pressed between two surfaces to which it will not ordinarily adhere,such as teflon, polyethylene, or silicone-treated surfaces and the like,until the resin particles have flowed together, fused and cured to arigid thermoset epoxy composition.

The composite laminates produced are very useful as furniture material,such as table-tops, desk-tops, cabinet components, and the like, but mayalso be used for counter tops, wall coverings, floor coverings, buildingpanels and the like.

The following examples set forth specific embodiments of the instantinvention. The invention, however, is not to be construed as beinglimited to these embodiments for there are, of course, numerous possiblevariations and modifications. All parts and percentages in the examples,as well as throughout the specification, are by weight unless otherwiseindicated.

EXAMPLE 1 200 parts ofa solid aromatic amine epoxy terminated adduct(Epon U52) parts of a solid aliphatic polyamine adduct (Epi- Cure 824)27 parts of a 25 percent solution of high molecular weight vinyl ethylether resin in mineral spirits (EDBN) 400 parts of VM&P naphtha Themixture was milled for 72 hours. The resultant dispersion was brushed ona 0.020 inch non-woven glass sheet (having continuous filaments whichhave been treated with a starch-oil binder) at a coating weight of about33 pounds per 1,000 sq. ft. The coated mat was allowed to dry at roomtemperature overnight and was then pressed in a heated platen press fortwo minutes at 100 psi and 300F., between one twentyfourth inch poplarveneer and three-fourths inch cedar particleboard. Upon removal from thepress, the resultant laminate exhibited excellent properties.

EXAMPLE 2 A vessel was charged with 75 parts of a tetrafunctionalpolyglycidyl ether of tetraphenylene ethane (Epon 1031) and 75 parts ofa solid diglycidyl ether of bisphenol A (Epon 1001) and the materialswere heated separately for 2 hours at 300F. to allow volatile materialsand dissolved gases to escape. A steel ball mill was then charged withthe above epoxies and 60 parts of an aniline formaldehyde aromatic amineadduct (Epi-Cure 844) 422.5 parts of cyclohexane and 4.5 parts of astyrene-butadiene-styrene block copolymer (Kraton 1 101 The compositionwas milled for 16 hours. The resultant composition was a creamy liquid.It was then brush-coated onto a 1 ounce per sq. ft. chopped strand glassfiber reinforcing mat, (Owens- Corning M-90l reinforcing mat) at acoating weight of about 66 pounds per 1,000 sq. ft. The coated mat wasallowed to dry 1 hour at room temperature followed by minutes at 120F.in a forced air oven. It was pressed in a heated platen pressimmediately and also after seven days aging at l20F., for three minutesat 300F. and 100 psi, between three-fourths inch particle board and onetwenty-eighth inch walnut veneer. The resulting laminates exhibitedexcellent properties.

The coated mat was also pressed between sheets of teflon film for 1minute at about 300F., and 500 psi and the cured impregnated matexhibited excellent physical properties.

EXAMPLE 3 An asbestos paper was impregnated by the following method:

A high shear mixer was charged with 10 parts of asbestos fiber and 2,000parts of water. To the dispersion were added 33 parts of a compositioncomprising 75 parts of Epon 1001, 75 parts of an octafunctional glycidylether, 45 parts of the aniline formaldehyde aromatic amine adduct ofExample 2, 4.5 parts of the styrene butadiene-styrene block copolymer ofExample 2, and 387.5 parts of cyclohexane.

While agitating 8 parts of a soap solution comprising 94 percent water,4-percent oleic acid, and 2 percent triethanolamine were added.

The slurry was poured on a screen and pressed between absorbent papersheets and dried. The resulting dry impregnated asbestos paper hadexcellent high strength properties after being pressed.

Although specific examples have been set forth above, it is not intendedthat the invention be limited solely thereto, but to include all of thevariations and modifications falling within the scope of the appendedclaims.

I claim:

1. A method of providing an adhesive material comprising coating orimpregnating a carrier with a composition comprising a blend of a roomtemperature solid epoxy resin averaging more than one l,2-epoxy groupper molecule, a room temperature solid epoxy reactive hardener in anamount sufficient to crosslink the epoxy resin, said resin and saidhardener constituting from 99 percent to 5% by weight of the totalsolids content, a film forming thermoplastic binder constituting from ito percent by weight of the total solids, and a dispersing mediumconstituting from 5 to 95 percent by weight of the entire saidcomposition which is a non-solvent for the epoxy and the hardener andwhich is a solvent or dispersant for the binder, and drying the coatingto a tack-free state.

2. The method of claim 1 wherein the carrier is fiberglass sheetmaterial.

3. The method of claim 1 wherein the carrier is asbestos sheet.

4. The method of claim 3 wherein the asbestos sheet is impregnated byforming a slurry of asbestos fibers in water and adding the compositionto the slurry and forming the composite into a sheet.

5. The method of claim ll wherein the hardener is a polymeric anilineformaldehyde aromatic amine adduct.

6. The method of claim 1 wherein the binder is astyrene-butadiene-styrene block copolymer.

7. The method of claim 1 wherein the dispersingmedium is cyclohexane.

8. The method of claim 1 wherein the epoxy resin is a solid diglycidylether of a polyhydric phenol.

9. An adhesive material comprising a carrier coated or impregnated witha material comprising a thermoplastic binder constituting l to 95percent by weight of said material having dispersed therein discretesolid particles of epoxy resin averaging more than one 1,2- epoxy groupper molecule and discrete solid particles of a heat reactivatable epoxyreactive hardener, said resin and said hardener together constitutingfrom 99 to 5 percent by weight of said adhesive material.

10. The adhesive material of claim 9 wherein the carrier is fiberglasssheet material.

H. The adhesive material of claim 9 wherein the hardener is an anilineformaldehyde aromatic amine adduct.

12. The adhesive material of claim 9 wherein the binder is astyrene-butadiene-styrene block copolymer.

13. The method of forming a laminate comprising (1) applying to acarrier a coating composition comprising a blend of a room temperaturesolid epoxy resin averaging more than one 1,2-epoxy group per molecule,a room temperature solid epoxy reactive hardener in an amount sufficientto crosslink the epoxy resin, said resin and hardener togetherconstituting from 99 to 5 percent by weight of the total solids content,a film forming thermoplastic binder constituting from 1 to 95 percent byweight of the total solids, and a dispersing medium constituting from 5to 95 percent by weight of the said composition which is a non-solventfor the epoxy and the hardener and a solvent or 16. The method of claim13 wherein the binder is a styrene-butadiene-styrene block copolymer.

17. The method of claim 13 wherein the hardener is an anilineformaldehyde aromatic amine adduct.

18. The method of claim 13 wherein the dispersing agent is cyclohexane.

19. The method of claim 13 wherein the epoxy resin is a solid diglycidylether of a polyhydric phenol.

2. The method of claim 1 wherein the carrier is fiberglass sheetmaterial.
 3. The method of claim 1 wherein the carrier is asbestossheet.
 4. The method of claim 3 wherein the asbestos sheet isimpregnated by forming a slurry of asbestos fibers in water and addingthe composition to the slurry and forming the composite into a sheet. 5.The method of claim 1 wherein the hardener is a polymeric anilineformaldehyde aromatic amine adduct.
 6. The method of claim 1 wherein thebinder is a styrene-butadiene-styrene block copolymer.
 7. The method ofclaim 1 wherein the dispersing medium is cyclohexane.
 8. The method ofclaim 1 wherein the epoxy resin is a solid diglycidyl ether of apolyhydric phenol.
 9. An adhesive material comprising a carrier coatedor impregnated with a material comprising a thermoplastic binderconstituting 1 to 95 percent by weight of said material having dispersedtherein discrete solid particles of epoxy resin averaging more than one1,2-epoxy group per molecule and discrete solid particles of a heatreactivatable epoxy reactive hardener, said resin and said hardenertogether constituting from 99 to 5 percent by weight of said adhesivematerial.
 10. The adhesive material of claim 9 wherein the carrier isfiberglass sheet material.
 11. The adhesive material of claim 9 whereinthe hardener is an aniline formaldehyde aromatic amine adduct.
 12. Theadhesive material of claim 9 wherein the binder is astyrene-butadiene-styrene block copolymer.
 13. The method of forming alaminate comprising (1) applying to a carrier a coating compositioncomprising a blend of a room temperature solid epoxy resin averagingmore than one 1,2-epoxy group per molecule, a room temperature solidepoxy reactive hardener in an amount sufficient to crosslink the epoxyresin, said resin and hardener together constituting from 99 to 5percent by weight of the total solids content, a film formingthermoplastic binder constituting from 1 to 95 percent by weight of thetotal solids, and a dispersing medium constituting from 5 to 95 percentby weight of the said composition which is a non-solvent for the epoxyand the hardener and a solvent or dispersing medium for the binder, (2)drying the coating to a tack-free film and, (3) placing a substrateagainst the coated side of the carrier and subjecting the composite to ahot pressing operation.
 14. The method of claim 13 wherein both sides ofthe carrier material are coated and two substrates are laminated to oneanother by pressing each substrate to a side of the coated carrier athigh temperature.
 15. The method of claim 13 wherein the carrier isfiberglass sheet material.
 16. The method of claim 13 wherein the binderis a styrene-butadiene-styrene block copolymer.
 17. The method of claim13 wherein the hardener is an aniline formaldehyde aromatic amineadduct.
 18. The method of claim 13 wherein the dispersing agent iscyclohexane.
 19. The method of claim 13 wherein the epoxy resin is asolid diglycidyl ether of a polyhydric phenol.